// SPDX-License-Identifier: GPL-2.0-or-later
/* kiocb-using read/write
 *
 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/uio.h>
#include <linux/sched/mm.h>
#include <linux/netfs.h>
#include "internal.h"

struct cachefiles_kiocb {
        struct kiocb            iocb;
        refcount_t              ki_refcnt;
        loff_t                  start;
        union {
                size_t          skipped;
                size_t          len;
        };
        netfs_io_terminated_t   term_func;
        void                    *term_func_priv;
        bool                    was_async;
};

static inline void cachefiles_put_kiocb(struct cachefiles_kiocb *ki)
{
        if (refcount_dec_and_test(&ki->ki_refcnt)) {
                fput(ki->iocb.ki_filp);
                kfree(ki);
        }
}

/*
 * Handle completion of a read from the cache.
 */
static void cachefiles_read_complete(struct kiocb *iocb, long ret, long ret2)
{
        struct cachefiles_kiocb *ki = container_of(iocb, struct cachefiles_kiocb, iocb);

        _enter("%ld,%ld", ret, ret2);

        if (ki->term_func) {
                if (ret >= 0)
                        ret += ki->skipped;
                ki->term_func(ki->term_func_priv, ret, ki->was_async);
        }

        cachefiles_put_kiocb(ki);
}

/*
 * Initiate a read from the cache.
 */
static int cachefiles_read(struct netfs_cache_resources *cres,
                           loff_t start_pos,
                           struct iov_iter *iter,
                           bool seek_data,
                           netfs_io_terminated_t term_func,
                           void *term_func_priv)
{
        struct cachefiles_kiocb *ki;
        struct file *file = cres->cache_priv2;
        unsigned int old_nofs;
        ssize_t ret = -ENOBUFS;
        size_t len = iov_iter_count(iter), skipped = 0;

        _enter("%pD,%li,%llx,%zx/%llx",
               file, file_inode(file)->i_ino, start_pos, len,
               i_size_read(file_inode(file)));

        /* If the caller asked us to seek for data before doing the read, then
         * we should do that now.  If we find a gap, we fill it with zeros.
         */
        if (seek_data) {
                loff_t off = start_pos, off2;

                off2 = vfs_llseek(file, off, SEEK_DATA);
                if (off2 < 0 && off2 >= (loff_t)-MAX_ERRNO && off2 != -ENXIO) {
                        skipped = 0;
                        ret = off2;
                        goto presubmission_error;
                }

                if (off2 == -ENXIO || off2 >= start_pos + len) {
                        /* The region is beyond the EOF or there's no more data
                         * in the region, so clear the rest of the buffer and
                         * return success.
                         */
                        iov_iter_zero(len, iter);
                        skipped = len;
                        ret = 0;
                        goto presubmission_error;
                }

                skipped = off2 - off;
                iov_iter_zero(skipped, iter);
        }

        ret = -ENOBUFS;
        ki = kzalloc(sizeof(struct cachefiles_kiocb), GFP_KERNEL);
        if (!ki)
                goto presubmission_error;

        refcount_set(&ki->ki_refcnt, 2);
        ki->iocb.ki_filp        = file;
        ki->iocb.ki_pos         = start_pos + skipped;
        ki->iocb.ki_flags       = IOCB_DIRECT;
        ki->iocb.ki_hint        = ki_hint_validate(file_write_hint(file));
        ki->iocb.ki_ioprio      = get_current_ioprio();
        ki->skipped             = skipped;
        ki->term_func           = term_func;
        ki->term_func_priv      = term_func_priv;
        ki->was_async           = true;

        if (ki->term_func)
                ki->iocb.ki_complete = cachefiles_read_complete;

        get_file(ki->iocb.ki_filp);

        old_nofs = memalloc_nofs_save();
        ret = vfs_iocb_iter_read(file, &ki->iocb, iter);
        memalloc_nofs_restore(old_nofs);
        switch (ret) {
        case -EIOCBQUEUED:
                goto in_progress;

        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /* There's no easy way to restart the syscall since other AIO's
                 * may be already running. Just fail this IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                ki->was_async = false;
                cachefiles_read_complete(&ki->iocb, ret, 0);
                if (ret > 0)
                        ret = 0;
                break;
        }

in_progress:
        cachefiles_put_kiocb(ki);
        _leave(" = %zd", ret);
        return ret;

presubmission_error:
        if (term_func)
                term_func(term_func_priv, ret < 0 ? ret : skipped, false);
        return ret;
}

/*
 * Handle completion of a write to the cache.
 */
static void cachefiles_write_complete(struct kiocb *iocb, long ret, long ret2)
{
        struct cachefiles_kiocb *ki = container_of(iocb, struct cachefiles_kiocb, iocb);
        struct inode *inode = file_inode(ki->iocb.ki_filp);

        _enter("%ld,%ld", ret, ret2);

        /* Tell lockdep we inherited freeze protection from submission thread */
        __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
        __sb_end_write(inode->i_sb, SB_FREEZE_WRITE);

        if (ki->term_func)
                ki->term_func(ki->term_func_priv, ret, ki->was_async);

        cachefiles_put_kiocb(ki);
}

/*
 * Initiate a write to the cache.
 */
static int cachefiles_write(struct netfs_cache_resources *cres,
                            loff_t start_pos,
                            struct iov_iter *iter,
                            netfs_io_terminated_t term_func,
                            void *term_func_priv)
{
        struct cachefiles_kiocb *ki;
        struct inode *inode;
        struct file *file = cres->cache_priv2;
        unsigned int old_nofs;
        ssize_t ret = -ENOBUFS;
        size_t len = iov_iter_count(iter);

        _enter("%pD,%li,%llx,%zx/%llx",
               file, file_inode(file)->i_ino, start_pos, len,
               i_size_read(file_inode(file)));

        ki = kzalloc(sizeof(struct cachefiles_kiocb), GFP_KERNEL);
        if (!ki)
                goto presubmission_error;

        refcount_set(&ki->ki_refcnt, 2);
        ki->iocb.ki_filp        = file;
        ki->iocb.ki_pos         = start_pos;
        ki->iocb.ki_flags       = IOCB_DIRECT | IOCB_WRITE;
        ki->iocb.ki_hint        = ki_hint_validate(file_write_hint(file));
        ki->iocb.ki_ioprio      = get_current_ioprio();
        ki->start               = start_pos;
        ki->len                 = len;
        ki->term_func           = term_func;
        ki->term_func_priv      = term_func_priv;
        ki->was_async           = true;

        if (ki->term_func)
                ki->iocb.ki_complete = cachefiles_write_complete;

        /* Open-code file_start_write here to grab freeze protection, which
         * will be released by another thread in aio_complete_rw().  Fool
         * lockdep by telling it the lock got released so that it doesn't
         * complain about the held lock when we return to userspace.
         */
        inode = file_inode(file);
        __sb_start_write(inode->i_sb, SB_FREEZE_WRITE);
        __sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);

        get_file(ki->iocb.ki_filp);

        old_nofs = memalloc_nofs_save();
        ret = vfs_iocb_iter_write(file, &ki->iocb, iter);
        memalloc_nofs_restore(old_nofs);
        switch (ret) {
        case -EIOCBQUEUED:
                goto in_progress;

        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /* There's no easy way to restart the syscall since other AIO's
                 * may be already running. Just fail this IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                ki->was_async = false;
                cachefiles_write_complete(&ki->iocb, ret, 0);
                if (ret > 0)
                        ret = 0;
                break;
        }

in_progress:
        cachefiles_put_kiocb(ki);
        _leave(" = %zd", ret);
        return ret;

presubmission_error:
        if (term_func)
                term_func(term_func_priv, -ENOMEM, false);
        return -ENOMEM;
}

/*
 * Prepare a read operation, shortening it to a cached/uncached
 * boundary as appropriate.
 */
static enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subrequest *subreq,
                                                      loff_t i_size)
{
        struct fscache_retrieval *op = subreq->rreq->cache_resources.cache_priv;
        struct cachefiles_object *object;
        struct cachefiles_cache *cache;
        const struct cred *saved_cred;
        struct file *file = subreq->rreq->cache_resources.cache_priv2;
        loff_t off, to;

        _enter("%zx @%llx/%llx", subreq->len, subreq->start, i_size);

        object = container_of(op->op.object,
                              struct cachefiles_object, fscache);
        cache = container_of(object->fscache.cache,
                             struct cachefiles_cache, cache);

        if (!file)
                goto cache_fail_nosec;

        if (subreq->start >= i_size)
                return NETFS_FILL_WITH_ZEROES;

        cachefiles_begin_secure(cache, &saved_cred);

        off = vfs_llseek(file, subreq->start, SEEK_DATA);
        if (off < 0 && off >= (loff_t)-MAX_ERRNO) {
                if (off == (loff_t)-ENXIO)
                        goto download_and_store;
                goto cache_fail;
        }

        if (off >= subreq->start + subreq->len)
                goto download_and_store;

        if (off > subreq->start) {
                off = round_up(off, cache->bsize);
                subreq->len = off - subreq->start;
                goto download_and_store;
        }

        to = vfs_llseek(file, subreq->start, SEEK_HOLE);
        if (to < 0 && to >= (loff_t)-MAX_ERRNO)
                goto cache_fail;

        if (to < subreq->start + subreq->len) {
                if (subreq->start + subreq->len >= i_size)
                        to = round_up(to, cache->bsize);
                else
                        to = round_down(to, cache->bsize);
                subreq->len = to - subreq->start;
        }

        cachefiles_end_secure(cache, saved_cred);
        return NETFS_READ_FROM_CACHE;

download_and_store:
        if (cachefiles_has_space(cache, 0, (subreq->len + PAGE_SIZE - 1) / PAGE_SIZE) == 0)
                __set_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags);
cache_fail:
        cachefiles_end_secure(cache, saved_cred);
cache_fail_nosec:
        return NETFS_DOWNLOAD_FROM_SERVER;
}

/*
 * Prepare for a write to occur.
 */
static int cachefiles_prepare_write(struct netfs_cache_resources *cres,
                                    loff_t *_start, size_t *_len, loff_t i_size)
{
        loff_t start = *_start;
        size_t len = *_len, down;

        /* Round to DIO size */
        down = start - round_down(start, PAGE_SIZE);
        *_start = start - down;
        *_len = round_up(down + len, PAGE_SIZE);
        return 0;
}

/*
 * Clean up an operation.
 */
static void cachefiles_end_operation(struct netfs_cache_resources *cres)
{
        struct fscache_retrieval *op = cres->cache_priv;
        struct file *file = cres->cache_priv2;

        _enter("");

        if (file)
                fput(file);
        if (op) {
                fscache_op_complete(&op->op, false);
                fscache_put_retrieval(op);
        }

        _leave("");
}

static const struct netfs_cache_ops cachefiles_netfs_cache_ops = {
        .end_operation          = cachefiles_end_operation,
        .read                   = cachefiles_read,
        .write                  = cachefiles_write,
        .prepare_read           = cachefiles_prepare_read,
        .prepare_write          = cachefiles_prepare_write,
};

/*
 * Open the cache file when beginning a cache operation.
 */
int cachefiles_begin_read_operation(struct netfs_read_request *rreq,
                                    struct fscache_retrieval *op)
{
        struct cachefiles_object *object;
        struct cachefiles_cache *cache;
        struct path path;
        struct file *file;

        _enter("");

        object = container_of(op->op.object,
                              struct cachefiles_object, fscache);
        cache = container_of(object->fscache.cache,
                             struct cachefiles_cache, cache);

        path.mnt = cache->mnt;
        path.dentry = object->backer;
        file = open_with_fake_path(&path, O_RDWR | O_LARGEFILE | O_DIRECT,
                                   d_inode(object->backer), cache->cache_cred);
        if (IS_ERR(file))
                return PTR_ERR(file);
        if (!S_ISREG(file_inode(file)->i_mode))
                goto error_file;
        if (unlikely(!file->f_op->read_iter) ||
            unlikely(!file->f_op->write_iter)) {
                pr_notice("Cache does not support read_iter and write_iter\n");
                goto error_file;
        }

        fscache_get_retrieval(op);
        rreq->cache_resources.cache_priv = op;
        rreq->cache_resources.cache_priv2 = file;
        rreq->cache_resources.ops = &cachefiles_netfs_cache_ops;
        rreq->cache_resources.debug_id = object->fscache.debug_id;
        _leave("");
        return 0;

error_file:
        fput(file);
        return -EIO;
}